Pulse-Combustion Boilers Reduce Condo's Electrical Consumption

Prior to the winter of 2009-2010, a 37-year-old, 250-hp boiler provided heat to The Lauren, a 168-unit condominium in Washington, D.C. According to Project Manager Walter Krolman, the unit functioned well, delivering plenty of heat throughout the 10-story building. However, Krolman questioned the boiler's efficiency.

"It was built for 80-percent efficiency," Krolman explained, "but it was probably functioning well below that level. So ... we decided to move forward and consider replacing the boiler ahead of schedule with a more efficient boiler, one that would immediately allow us to capture energy savings and convert those savings to reduced operating costs."

The task of finding a new, more efficient boiler fell to Jack McNabb, a consulting engineer who had worked on a variety of projects related to The Lauren's mechanical and electrical systems. McNabb was not surprised to find the original boiler was oversized. At the time it was installed, he said, energy costs were low, and the prevailing practice was to oversize systems to ensure an adequate heat supply.

"Consequently, The Lauren ended up with a boiler that was approximately 8 ft in diameter and more than 20 ft long and operating at about 62-percent efficiency as recently as last year," McNabb said. "It was an enormous tank of hot water radiating heat to the world."

The boiler filled the building's pipes with hot water for heating during winter, while a 220-ton chiller filled them with cold water for cooling during summer. Stack-style fan-coil units delivered heat and cooling to the condominium, while separate gas-fired hot-water heaters provided domestic hot water.

In his search for greater efficiency, McNabb turned to condensing boilers.

"These boilers are traditionally the most efficient," McNabb explained. "And as I looked at various manufacturers, I noted Fulton was among them. I knew the Fulton name, ... so I looked a little closer at Fulton boilers and was introduced to pulse-combustion technology."

Pulse combustion is widely recognized as one of the most efficient ways to burn fuel. A pulse is defined as one cycle of ignition and combustion of a gas/air mixture in a specially designed chamber.

"It definitely makes for an energy-efficient boiler," Josh Rossman, a sales associate for United Energy Products Inc., the firm that supplied two Fulton Pulse boilers to The Lauren, said. "But just as importantly, a pulse boiler significantly reduces electrical consumption associated with the boiler. In fact, the boiler consumes almost no power while in operation."

The pulse-combustion process is naturally aspirated and does not require a blower motor for operation. An assist fan is used for pre/post purge only and turns off once combustion is established. Pulse boilers require electricity only for purge cycles, powering fuel valves, control, and other safety features. The pulse-combustion process itself requires no electricity.

The two Fulton Pulse boilers McNabb recommended for The Lauren are natural-gas-fired, 1.4-million-Btuh-input units rated at 89- to 98-percent efficiency over the majority of load-matching conditions.

"The trick in applying these boilers is that the less they're loaded up, the more efficient they become," McNabb said. "By installing two boilers and sharing the load, The Lauren is averaging about 94-percent seasonal efficiency over the load range. And we have built-in redundancy, should we need it, for increased reliability."

The boilers operate with Fulton's ModSync control system, which regulates the temperature of water leaving a boiler based on outdoor temperature.

"The system turns on the lead boiler when it needs to fire," McNabb explained. "As long as it can carry this load, it will. But when the temperature drops to a predetermined point, the system automatically turns on the second boiler, allowing both boilers to operate at a lower, more efficient load. That's the point where efficiency really starts to kick in because both boilers jockey for a lower load when that second boiler kicks in."

McNabb's recommendation to The Lauren included cost and savings estimates. According to Krolman, the recommendation was thorough.

The boilers were installed at the beginning of the 2009-2010 heating season. A heating season later, they were exceeding expectations for performance. The Pulse boilers are wringing more heat from the combustion process, as evidenced by the temperature of flue gases: approximately 150°F, as opposed to 300°F in a conventional boiler system.

"The Lauren saved approximately 32 percent in gas consumption, or 12,200 therms, during the heating season," McNabb said. "To give you a dollar value, The Lauren is paying about $1.50 per therm ..., so that amounts to about $18,300 saved per heating season.

"And the electrical savings are substantial, too," McNabb continued. "The fan associated with the old boiler ran all the time that the boiler burner operated, costing somewhere around $2,000 a heating season. The new system uses a smaller fan, which draws just 4 amps at 120 v and is used only for a 30-sec purge, consuming substantially less electricity and reducing the operating cost of the boilers. When running, the Pulse boilers consume about 0.75 amps."

According to McNabb, the pulse-combustion system contributed to a simpler mechanical design. First, the boilers are much smaller than the one they replaced—approximately 3½-ft wide by 6-ft tall and 4-ft deep—leaving additional unused space in the mechanical room.

"And because the Pulse boiler is more efficient, the flue gases take up less volume," McNabb said. "As a result, flue pipes are much smaller than with a conventional boiler—as much as 2/3 to 50-percent smaller—which makes the pipes much easier to lay out."

Savings and comfort are what have impressed Krolman and the residents of The Lauren most.

"We experienced a fairly severe winter last year, but our building was always warm," Krolman said. "It's also quiet. My office is right next to the mechanical room, and I don't hear the boilers.

"It's just a nice, solid installation," Krolman concluded. "The boilers have done what they were projected to do. In fact, they surpassed those projections and have created a good amount of customer satisfaction in the process."

Information and photographs courtesy of The Fulton Cos.

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